Variable gate lengths for vertical transistors

ABSTRACT

The method includes prior to depositing a gate on a first vertical FET on a semiconductor substrate, depositing a first layer on the first vertical FET on the semiconductor substrate. The method further includes prior to depositing a gate on a second vertical FET on the semiconductor substrate, depositing a second layer on the second vertical FET on the semiconductor substrate. The method further includes etching the first layer on the first vertical FET to a lower height than the second layer on the second vertical FET. The method further includes depositing a gate material on both the first vertical FET and the second vertical FET. The method further includes etching the gate material on both the first vertical FET and the second vertical FET to a co-planar height.

BACKGROUND

The present invention relates generally to the field of semiconductordevices, and more particularly to the formation of modified gatelengths.

The fabrication of semiconductor devices involves forming electroniccomponents in and on semiconductor substrates, such as silicon wafers.These electronic components may include one or more conductive layers,one or more insulation layers, and doped regions formed by implantingvarious dopants into portions of a semiconductor substrate to achievespecific electrical properties. Semiconductor devices includetransistors, resistors, capacitors, and the like, with intermediate andoverlying metallization patterns at varying levels, separated bydielectric materials, which interconnect the semiconductor devices toform integrated circuits.

Field-effect transistors (FETs), such as metal-oxide-semiconductor FETs(MOSFETs), are a commonly used semiconductor device. Generally, a FEThas three terminals, i.e., a gate structure (or gate stack), a sourceregion, and a drain region. In some instances, the body of thesemiconductor may be considered a fourth terminal. The gate stack is astructure used to control output current, i.e., flow of carriers in thechannel portion of a FET, through electrical or magnetic fields. Thechannel portion of the substrate is the region between the source regionand the drain region of a semiconductor device that becomes conductivewhen the semiconductor device is turned on. The source region is a dopedregion in the semiconductor device from which majority carriers areflowing into the channel portion. The drain region is a doped region inthe semiconductor device located at the end of the channel portion, inwhich carriers are flowing into from the source region via the channelportion and out of the semiconductor device through the drain region. Aconductive plug, or contact, is electrically coupled to each terminal.One contact is made to the source region, one contact is made to thedrain region, and one contact is made to the gate stack.

A multigate device or multiple gate field-effect transistor (MuGFET)refers to a MOSFET (metal-oxide-semiconductor field-effect transistor)which incorporates more than one gate into a single device. The multiplegates may be controlled by a single gate electrode, wherein the multiplegate surfaces act electrically as a single gate, or by independent gateelectrodes. A multigate device employing independent gate electrodes issometimes called a Multiple Independent Gate Field Effect Transistor(MIGFET).

SUMMARY

One aspect of the present invention discloses a method for fabricationof a field-effect transistor (FET) structure. The method includes priorto depositing a gate on a first vertical FET on a semiconductorsubstrate, depositing a first layer on the first vertical FET on thesemiconductor substrate. The method further includes prior to depositinga gate on a second vertical FET on the semiconductor substrate,depositing a second layer on the second vertical FET on thesemiconductor substrate. The method further includes etching the firstlayer on the first vertical FET to a lower height than the second layeron the second vertical FET. The method further includes depositing agate material on both the first vertical FET and the second verticalFET. The method further includes etching the gate material on both thefirst vertical FET and the second vertical FET to a co-planar height.

Another aspect of the present invention discloses a method forfabrication of a field-effect transistor (FET) structure. The methodincludes depositing a first layer of gate materials on a first verticalFET on a semiconductor substrate. The method further includes depositinga second layer of gate materials on a second vertical FET on thesemiconductor substrate. The method further includes wherein the bottomof the first layer and the bottom of the second layer are co-planar. Themethod further includes etching the first layer of gate materials on thefirst vertical FET. The method further includes etching the second layerof gate materials on the second vertical FET. The method furtherincludes wherein the top of the first layer of gate materials and thetop of the second layer of gate materials are not co-planar.

Another aspect of the present invention discloses a field-effecttransistor (FET) structure. The FET structure comprises a first verticalfield effect transistor (FET) formed on a semiconductor substrate and asecond vertical FET formed on the semiconductor substrate. The structurefurther comprises the first vertical FET with a gate height co-planar toa gate height of the second vertical FET. The structure furthercomprises the first vertical FET comprising a first layer below a gateon the first vertical FET. The structure further comprises the secondvertical FET comprising second layer below a gate on the second verticalFET. The structure further comprises wherein the first layer below thegate on the first vertical FET and the second layer below the gate onthe second vertical FET are comprised of a first semiconductor material.The structure further comprises wherein the layer below the gate on thesecond vertical FET is not co-planar with the layer below the gate onthe first vertical FET. The structure further comprises wherein thebottom of the gate on the first vertical FET is not co-planar with thebottom of the gate on the second vertical FET.

Another aspect of the present invention discloses a field-effecttransistor (FET) structure. The FET structure comprises a first verticalfield effect transistor (FET) formed on a semiconductor substrate and asecond vertical FET formed on the semiconductor substrate. The structurefurther comprises the first vertical FET with a gate height that is notco-planar to a gate height of the second vertical FET. The methodfurther comprises the first vertical FET comprising a first layer abovea gate on the first vertical FET. The method further comprises thesecond vertical FET comprising a second layer above a gate on the secondvertical FET. The method further comprises wherein the bottom of thegate on the first vertical FET is co-planar with the bottom of the gateon the second vertical FET.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the disclosure solely thereto, will best beappreciated in conjunction with the accompanying drawings, in which:

FIG. 1 depicts a cross section view of a vertical transistor, inaccordance with embodiments of the invention.

FIG. 2A depicts a cross section view of one quarter of a verticaltransistor, in accordance with an embodiment of the present invention.FIG. 2B depicts a cross section view of one quarter of a verticaltransistor in which the bottom S/D has been etched for a longer period,in accordance with embodiments of the present invention.

FIG. 3A depicts a cross section view of one quarter of a verticaltransistor, in accordance with an embodiment of the present invention.FIG. 3B depicts a cross section view of one quarter of a verticaltransistor in which the bottom spacer has been etched for a longerperiod, in accordance with embodiments of the present invention.

FIG. 4A depicts a cross section view of one quarter of a verticaltransistor, in accordance with an embodiment of the present invention.FIG. 4B depicts a cross section view of one quarter of a verticaltransistor in which the HiK foot and/or WF metal has been etched for alonger period, in accordance with embodiments of the present invention.

FIG. 5A depicts a cross section view of one quarter of a verticaltransistor, in accordance with an embodiment of the present invention.FIG. 5B depicts a cross section view of one quarter of a verticaltransistor in which the gate top and/or WF metal has been etched for alonger period, in accordance with embodiments of the present invention.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely illustrative of the claimed structures and methods that maybe embodied in various forms. In addition, each of the examples given inconnection with the various embodiments is intended to be illustrativeand not restrictive. Further, the Figures are not necessarily to scale,some features may be exaggerated to show details of particularcomponents. Therefore, specific structural and functional detailsdisclosed herein are not to be interpreted as limiting but merely as arepresentative basis for teaching one skilled in the art to variouslyemploy the methods and structures of the present disclosure.

References in the specification to “one embodiment,” “an embodiment,”“an example embodiment,” etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to affect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

For purposes of the description hereinafter, the terms “upper,” “lower,”“right,” “left,” “vertical,” “horizontal,” “top,” “bottom,” andderivatives thereof shall relate to the disclosed structures andmethods, as oriented in the drawing figures. The terms “overlying,”“atop,” “on,” “positioned on,” or “positioned atop” mean that a firstelement, such as a first structure, is present on a second element, suchas a second structure, wherein intervening elements, such as aninterface structure may be present between the first element and thesecond element. The term “direct contact” means that a first element anda second element are connected without any intermediary conducting,insulating, or semiconductor layers at the interface of the twoelements.

Embodiments of the present invention recognize that multiple gatelengths is a popular feature to allow different Ion (on-state current)vs. Ioff (off-state current) device points. Embodiments of the presentinvention recognize that supporting multiple gate lengths is extremelydifficult at the 7 nm node and beyond with lateral transistors due topoor Ioff with shorter gates and longer gates resulting in increasedcontacts resistance. Embodiments of the present invention recognize thatmoving to a vertical transistor allows for room to support multiple gatelengths.

Implementation of embodiments of the invention may take a variety offorms, and exemplary implementation details are discussed subsequentlywith reference to the Figures.

FIG. 1 depicts a cross section view of an embodiment of verticaltransistor 100, in accordance with the present invention. Verticaltransistor 100 may include more or less layers than depicted and isshown to represent a generic vertical transistor as known in the art. Insome embodiments, vertical transistor 100 may include a single gatedesign, a multiple gate design, or a wraparound gate design. Layer 102represents the base of the structure. In some embodiments, layer 102 maybe a silicon wafer or any other base structure known in the art. Layer104 represents the bottom source or drain of vertical transistor 100. Insome embodiments, a designer of vertical transistor 100 may require asource or a drain at the bottom of vertical transistor 100 depending onthe desired direction of flow across the channel (e.g., channel 114). Inan embodiment, layer 104 may be a heavily doped source or drain. Layer120 may be composed of a first semiconductor layer material with thesame doping polarity as the device polarity. In some examples, thesource/drain layer, (e.g. layer 120) may comprise a number of basesemiconductor material as well as dopants. For example, layer 120 maycomprise silicon, tellurium, selenium, or other n-type doping materials.In another example, layer 120 may comprise p-type doping materials. Inyet another example, layer 120 may be doped using conventional methods,such as ion implantation or any other method known by a person skilledin the art.

Layer 106 may be a bottom spacer utilized to insulate the gate from thebottom source or drain to prevent shorting. In an example, a spacer maybe a dielectric material, such as SiN (Silicon Nitride), a nitridecompound dielectric material, or an oxide, such as SiO₂. In someembodiments, layer 106 may be etched smaller or not deposited, which mayallow for an increase in the gate length (e.g., gate 112). In someembodiments, layer 108 may be a HiK (high K) dielectric (e.g., high Kdielectric may be deposited chemical vapor deposition (CVD), atomiclayer deposition (ALD), physical vapor deposition (PVD), or othersimilar deposition methods). Some examples of HiK materials may includeHfO₂, ZrO₂, AL₂O₃, TiO₂, LaAlO₃, HfSiO₂, Y₂O₃, etc. In some embodiments,layer 108 may be etched to reduce or remove the bottom portion of layer108. In some embodiments, vertical transistor 100 may include anadditional gate dielectric between layer 108 and channel 114, such aslayer 110. In an example, layer 110 may include a dielectric material,such as SiN (Silicon Nitride), a nitride compound dielectric material,or an oxide, such as SiO₂.

In some embodiments, gate 112 may include a work function metal and alow resistance metal. In an example, the work function metal maycomprise the inner surface of gate 112 where gate 112 contacts the HiKlayer of 108. In some embodiments, gate 112 may be etched to reach adesired gate height. Some examples of materials utilized in gate 112 mayinclude TiN, W, Ta, TaN, Au, etc. An example of a work function metalutilized in gate 112 may include TiN, TiC, TiAlC, etc.

In some embodiments, channel 114 is a highly conductive region betweenthe source and the drain (e.g., layer 104 and layer 120) of verticaltransistor 100. In some embodiments, channel 114 may be a low bandgapchannel utilizing materials, such as SiGe, GaAs, InAs, or an alloy ofInGaAs, or another group IV semiconductor commonly used in the art. Invarious embodiments, layer 116 is a top spacer similar to layer 106. Inan example, layer 116 may include a dielectric material, such as SiN(Silicon Nitride), a nitride compound dielectric material, or an oxide,such as SiO2. In some embodiments, layer 120 is a top source or drain,such as a heavily doped source or drain. Layer 120 may be composed of afirst semiconductor layer material with the same doping polarity as thedevice polarity. For example, layer 120 may comprise silicon, tellurium,selenium, or other n-type doping materials. In another example, layer120 may comprise p-type doping materials. In yet another example, layer120 may be doped using conventional methods, such as ion implantation orany other method known by a person skilled in the art. In an example,layer 104 is a source; and therefore, layer 120 is a drain. In anotherexample, layer 104 is a drain; and therefore, layer 120 is a source. Invarious embodiments, layer 122 is a dielectric material, such as SiN orSi0₂, that enables the source to be contained above the gate (e.g., gate112) and channel (e.g., channel 114) in vertical transistor 100.

FIGS. 2A and 2B represent devices 200 and 250 located on the same wafer.FIG. 2A depicts a cross section view of one quarter of a verticaltransistor, in accordance with an embodiment of the present invention.FIG. 2B depicts a cross section view of one quarter of a verticaltransistor in which the bottom S/D has been etched for a longer period,in accordance with embodiments of the present invention. In someembodiments, etching may be performed by utilizing reactive ion etching(RIE) or other methods known by a person skilled in the art.

FIG. 2A is representative of a cross section of a vertical transistor.In some embodiments, FIG. 2A may be a generic representation of verticaltransistor 100. FIG. 2A includes a base 202, which is the semiconductorsubstrate (e.g., silicon) the vertical transistor is constructed on.FIG. 2A also includes a bottom source or drain located within verticaltransistor 204 and a top source or drain located in top layer 206. FIG.2A includes bottom spacer 208 which corresponds to layer 106 fromFIG. 1. FIG. 2A further includes HiK gate dielectric 210 thatcorresponds to layer 108 in FIG. 1, gate WF (work function) metal 212and gate metal 214 that corresponds to gate 112 in FIG. 1, and topspacer 216 that corresponds to layer 116 in FIG. 1.

FIG. 2B depicts a cross section view representing the difference betweena standard vertical transistor (e.g., 200 from FIG. 2A) and a modifiedvertical transistor (e.g., 250 from FIG. 2B) to adjust the gate length.In FIG. 2B, the bottom source or drain represented at the bottom portionof vertical transistor 254, and also corresponding to layer 104 in FIG.1, can be etched to different lengths. In an example, device 200 of FIG.2A is masked and device 250 of FIG. 2B is selectively etched. By maskingthe device 200 of FIG. 2A prior to the selective etching, device 200remains unchanged while device 250 is etched. By etching the bottomsource or drain (e.g., the lower portion of vertical transistor 254) thegate length can be extended while keeping the same overall height forFIG. 2B as in FIG. 2A (e.g., the tops of gate metals 214 and 264 areco-planar). In an embodiment, the bottom source or drain of device 250is selectively etched. After a spacer and HiK gate dielectric are added,gate materials are then added to both devices 200 and 250, which aresubsequently etched to the same gate height resulting in a longer gatefor device 250.

In an example, the bottom source or drain of vertical transistor 254 hasbeen etched lower relative to the bottom source or drain of verticaltransistor 204. Bottom spacer 258 is added via process that grows,coats, or otherwise transfers a material onto the wafer, such as PVD,CVD, etc., in the same amount as bottom spacer 208 in FIG. 2A. HiK gatedielectric 260 is added similar to HiK gate dielectric 210 in FIG. 2A;however, HiK gate dielectric 260 and HiK gate dielectric 210 are etchedto a co-planar level. In an example, HiK gate dielectric 210 and HiKgate dielectric 260 are added to devices 200 and 250 in an “overflow”amount, and then etched back to a desired co-planer level. Gate WF metal262 and gate metal 264 are added in the same manner as gate WF metal 212and gate metal 214 in FIG. 2A; however, gate WF metal 212 and gate WFmetal 262 are etched to a co-planar level. In an example, gate WF metal212 and gate WF metal 262 are added to devices 200 and 250 in an“overflow” amount and then etched back to a desired co-planer level. Topspacer 266 is added to cover the top of the gates as in top spacer 216in FIG. 2A; however, top spacer 216 and top spacer 266 are etched to aco-planar level. In an example, top spacer 216 and top spacer 266 areadded to devices 200 and 250 in an “overflow” amount and then etchedback to a desired co-planer level. Top layer 256 represents the topsource or drain in FIG. 2B, which is the same size as top layer 206 inFIG. 2A.

FIGS. 3A and 3B represent devices 300 and 350 located on the same wafer.FIG. 3 depicts a cross section view of one quarter of a verticaltransistor, in accordance with an embodiment of the present invention.FIG. 3B depicts a cross section view of one quarter of a verticaltransistor in which the bottom spacer has been etched for a longerperiod, in accordance with embodiments of the present invention. In someembodiments, etching may be performed by utilizing reactive ion etching(RIE) or other methods known by a person skilled in the art.

FIG. 3A is representative of a cross section of a vertical transistor.In some embodiments, FIG. 3A may be a generic representation of verticaltransistor 100. FIG. 3A includes a base 302, which is the semiconductorsubstrate (e.g., silicon) the vertical transistor is constructed on.FIG. 3A also includes a bottom source or drain located within verticaltransistor 304 and a top source or drain located in top layer 306. FIG.3A includes bottom spacer 308 which corresponds to layer 106 fromFIG. 1. FIG. 3A further includes HiK gate dielectric 310 thatcorresponds to layer 108 in FIG. 1, gate WF (work function) metal 312and gate metal 314 that corresponds to gate 112 in FIG. 1, and topspacer 316 that corresponds to layer 116 in FIG. 1.

FIG. 3B depicts a cross section view representing the difference betweena standard vertical transistor (e.g., device 300 from FIG. 3A) and amodified vertical transistor (e.g., device 350 from FIG. 3B) to adjustthe gate length. In FIG. 3B, the bottom source or drain represented atthe bottom portion of vertical transistor 354, and also corresponding tolayer 104 in FIG. 1, which is maintained as the same size as in FIG. 3A.In an embodiment, by etching the bottom spacer (e.g., bottom spacer notshown because it has been etched to completely remove the spacer in FIG.3B or layer 106 in FIG. 1) the gate length can be extended while keepingthe same overall height for FIG. 3B as in FIG. 3A. In an embodiment, thebottom spacer of device 350 from FIG. 3B is etched more. In an example,the bottom spacer (e.g., bottom spacer 358) of device 300 of FIG. 3A ismasked and device 350 of FIG. 3B is selectively etched. By maskingdevice 300 of FIG. 3A prior to the selective etching, device 300 remainsunchanged while device 350 is etched. By etching the bottom spacer(e.g., bottom spacer 358) the gate length can be extended while keepingthe same overall height for FIG. 3B as in FIG. 3A (e.g., the tops ofgate metals 314 and 364 are co-planar). In an embodiment, the bottomspacer of FIG. 3B, device 350 is selectively etched. Gate materials arethen added to both devices 300 and 350, which are subsequently etched tothe same gate height resulting in a longer gate for device 350.

In an example, bottom spacer 358 has been etched lower relative tobottom spacer 308. In another example, bottom spacer 358 may not beadded or bottom spacer 358 is etched (e.g., RIE etched) to remove bottomspacer 358 completely. HiK gate dielectric 360 is added similar to HiKgate dielectric 310 in FIG. 3A; however, HiK gate dielectric 360 and HiKgate dielectric 310 are etched to a co-planar level. In an example, HiKgate dielectric 310 and HiK gate dielectric 360 are added to devices 300and 350 in an “overflow” amount and then etched back to a desiredco-planer level. Gate WF metal 362 and gate metal 364 are added in thesame manner as gate WF metal 312 and gate metal 314 in FIG. 3A; however,gate WF metal 312 and gate WF metal 362 are etched to a co-planar level.In an example, gate WF metal 312 and gate WF metal 362 are added todevices 300 and 350 in an “overflow” amount and then etched back to adesired co-planer level. Top spacer 366 is added by the same method tocover the top of the gates as in top spacer 316 in FIG. 3A; however, topspacer 316 and top spacer 366 are etched to a co-planar level. In anexample, top spacer 316 and top spacer 366 are added to devices 300 and350 in an “overflow” amount and then etched back to a desired co-planerlevel. Top layer 356 represents the top source or drain in FIG. 3B,which is the same size as top layer 306 in FIG. 3A.

FIGS. 4A and 4B represent devices 400 and 450 located on the same wafer.FIG. 4A depicts a cross section view of one quarter of a verticaltransistor, in accordance with an embodiment of the present invention.FIG. 4B depicts a cross section view of one quarter of a verticaltransistor in which the HiK gate dielectric has been etched for a longerperiod, in accordance with embodiments of the present invention. In someembodiments, etching may be performed by utilizing reactive ion etching(RIE) or other methods known by a person skilled in the art.

FIG. 4A is representative of a cross section of a vertical transistor.In some embodiments, FIG. 4A may be a generic representation of verticaltransistor 100. FIG. 4A includes a base 402, which is the semiconductorsubstrate (e.g., silicon) the vertical transistor is constructed on.FIG. 4A also includes a bottom source or drain located within verticaltransistor 404 and a top source or drain located in top layer 406. FIG.4A includes bottom spacer 408 which corresponds to layer 106 fromFIG. 1. FIG. 4A further includes HiK gate dielectric 410 thatcorresponds to layer 108 in FIG. 1, gate WF (work function) metal 412and gate metal 414 that corresponds to gate 112 in FIG. 1, and topspacer 416 that corresponds to layer 116 in FIG. 1.

FIG. 4B depicts a cross section view representing the difference betweena standard vertical transistor (e.g., device 400 from FIG. 4A) and amodified vertical transistor (e.g., device 450 from FIG. 4B) to adjustthe gate length. In FIG. 4B, the bottom source or drain represented atthe bottom portion of vertical transistor 454, and also corresponding tolayer 104 in FIG. 1, which is maintained as the same size as in FIG. 4A.Bottom spacer 458 is added in the same amount as bottom spacer 408 inFIG. 4A. In an embodiment, by etching the HiK gate dielectric (e.g., HiKgate dielectric 460 in FIG. 4B or layer 108 in FIG. 1) the gate lengthcan be extended while keeping the same overall height for FIG. 4B as inFIG. 4A. In an embodiment, the HiK gate dielectric of FIG. 4B is etchedmore. In an example, the HiK gate dielectric (e.g., HiK gate dielectric410) of device 400 of FIG. 4A is masked and device 450 of FIG. 4B isselectively etched. By masking device 400 of FIG. 4A prior to theselective etching, device 400 remains unchanged while device 450 isetched. By etching the HiK gate dielectric (e.g., HiK gate dielectric460) the gate length can be extended while keeping the same overallheight for FIG. 4B as in FIG. 4A (e.g., the tops of gate metals 414 and464 are co-planar). In an embodiment, the HiK gate dielectric of FIG. 4Bdevice 450 is selectively etched. Gate materials are then added to bothdevices 400 and 450, which are subsequently etched to the same gateheight resulting in a longer gate for device 450.

In an example, HiK gate dielectric 460 has been etched lower relative toHiK gate dielectric 410. In another example, HiK gate dielectric 460 maynot be added or etched to remove bottom portion of HiK gate dielectric460 completely. Gate WF metal 462 and gate metal 464 are added in thesame manner as gate WF metal 412 and gate metal 414 in FIG. 4A; however,gate WF metal 412 and gate WF metal 462 are etched to a co-planar level.In an example, gate WF metal 412 and gate WF metal 462 are added todevices 400 and 450 in an “overflow” amount and then etched back to adesired co-planer level. Top spacer 466 is added by the same method tocover the top of the gates as in top spacer 416 in FIG. 4A; however, topspacer 416 and top spacer 466 are etched to a co-planar level. In anexample, top spacer 416 and top spacer 466 are added to devices 400 and450 in an “overflow” amount and then etched back to a desired co-planerlevel. Top layer 456 represents the top source or drain in FIG. 4B,which is the same size as top layer 406 in FIG. 4A.

FIGS. 5A and 5B represent devices 500 and 550 located on the same wafer.FIG. 5A depicts a cross section view of one quarter of a verticaltransistor, in accordance with an embodiment of the present invention.FIG. 5B depicts a cross section view of one quarter of a verticaltransistor in which the gate metal has been etched for a longer period,in accordance with embodiments of the present invention. In someembodiments, etching may be performed by utilizing reactive ion etching(RIE) or other methods known by a person skilled in the art.

FIG. 5A is representative of a cross section of a vertical transistor.In some embodiments, FIG. 5A may be a generic representation of verticaltransistor 100. FIG. 5A includes a base 502, which is the semiconductorsubstrate (e.g., silicon) the vertical transistor is constructed on.FIG. 5A also includes a bottom source or drain located within verticaltransistor 504 and a top source or drain located in top layer 506. FIG.5A includes bottom spacer 508 which corresponds to layer 106 fromFIG. 1. FIG. 5A further includes HiK gate dielectric 510 thatcorresponds to layer 108 in FIG. 1, gate WF (work function) metal 512and gate metal 514 that corresponds to gate 112 in FIG. 1, and topspacer 516 that corresponds to layer 116 in FIG. 1.

FIG. 5B depicts a cross section view representing the difference betweena standard vertical transistor (e.g., device 500 from FIG. 5A) and amodified vertical transistor (e.g., device 550 from FIG. 5B) to adjustthe gate length. In FIG. 5B, the bottom source or drain represented atthe bottom portion of vertical transistor 554, and also corresponding tolayer 104 in FIG. 1, which is maintained as the same size as in FIG. 5A.Bottom spacer 558 is added in the same amount as bottom spacer 508 inFIG. 5A. HiK gate dielectric 560 is added similar to HiK gate dielectric510 in FIG. 5A. In an embodiment, by etching the gate WF metal (e.g.,gate WF metal 562 in FIG. 5 or gate 112 in FIG. 1) and/or gate metal(e.g., gate metal 564 in FIG. 5 or gate 112 in FIG. 1) the gate lengthcan be shortened while keeping the same overall height for FIG. 5B as inFIG. 5A. In an embodiments, gate WF metal 562 and/or gate metal 564 ofFIG. 5B are etched more. In an example, the gate WF metal and/or gatemetal (e.g., gate WF metal 512 and/or gate metal 514) of device 500 ofFIG. 5A is masked and device 550 of FIG. 5B is selectively etched. Bymasking device 500 of FIG. 5A prior to the selective etching, device 500remains unchanged while device 550 is etched. By etching the gate WFmetal and/or gate metal (e.g., gate WF metal 562 and/or gate metal 564)the gate length can be shortened while keeping the same overall heightfor FIG. 5B as in FIG. 5A (e.g., the tops of gate metals 514 and 564 areco-planar).

In an example, gate metal 564 has been etched lower relative to gatemetal 514. In another example, gate WF metal 562 has been etched lowerrelative to gate WF metal 512. In yet another example, both gate metal564 and gate WF metal 562 have been etched lower. Top spacer 566 isadded by the same method to cover the top of the gates as in top spacer516 in FIG. 4A; however, top spacer 516 and top spacer 566 are etched toa co-planar level. In an example, top spacer 516 and top spacer 566 areadded to devices 500 and 550 in an “overflow” amount and then etchedback to a desired co-planer level. Top layer 556 represents the topsource or drain in FIG. 5B, which is the same size as top layer 506 inFIG. 5A.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration but are not intended tobe exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the invention.The terminology used herein was chosen to best explain the principles ofthe embodiment, the practical application or technical improvement overtechnologies found in the marketplace, or to enable others of ordinaryskill in the art to understand the embodiments disclosed herein.

1. A semiconductor structure comprising: a first vertical field effecttransistor (FET) formed on a semiconductor substrate and a secondvertical FET formed on the semiconductor substrate; the first verticalFET with a gate height co-planar to a gate height of the second verticalFET; the first vertical FET comprising a first layer below a gate on thefirst vertical FET; the second vertical FET comprising a second layerbelow a gate on the second vertical FET; wherein the first verticalfield effect transistor (FET) formed on a semiconductor substrate andthe second vertical FET formed on the semiconductor substrate include agate WF metal layer that is below and beside the gate on the firstvertical FET and the gate on the second vertical FET; wherein the firstlayer below the gate on the first vertical FET and the second layerbelow the gate on the second vertical FET are comprised of a firstsemiconductor material; wherein the layer below the gate on the secondvertical FET is not co-planar with the layer below the gate on the firstvertical FET; and wherein the bottom of the gate on the first verticalFET is not co-planar with the bottom of the gate on the second verticalFET.
 2. The structure of claim 1, wherein the first layer below the gateon the first vertical FET and the second layer below the gate on thesecond vertical FET comprise a source, wherein the top of the sourceunder the gate of the first vertical FET and the top of the source underthe gate of the second vertical FET are not co-planar.
 3. The structureof claim 1, wherein the first layer below the gate on the first verticalFET and the second layer below the gate on the second vertical FETcomprise a drain, wherein the top of the drain under the gate of thefirst vertical FET and the top of the drain under the gate of the secondvertical FET are not co-planar.
 4. (canceled)
 5. The structure of claim1, wherein the first layer below the gate on the first vertical FET andthe second layer below the gate on the second vertical FET comprise ahigh K dielectric, wherein the high K dielectric of the first verticalFET and the high K dielectric of the second vertical FET are a differentthickness. 6-24. (canceled)
 25. A semiconductor structure comprising: afirst vertical field effect transistor (FET) formed on top of asemiconductor substrate and a second vertical FET formed on thesemiconductor substrate, wherein a source or drain is formed directly ontop of the semiconductor substrate; the first vertical FET with a gateheight co-planar to a gate height of the second vertical FET; the firstvertical FET comprising a first layer below a gate on the first verticalFET; the second vertical FET comprising a second layer below a gate onthe second vertical FET; wherein the first layer below the gate on thefirst vertical FET and the second layer below the gate on the secondvertical FET are comprised of a first semiconductor material; whereinthe second layer below the gate on the second vertical FET is notco-planar with the layer below the gate on the first vertical FET; andwherein the bottom of the gate on the first vertical FET is notco-planar with the bottom of the gate on the second vertical FET.